The present invention relates to pressure sensitive adhesive compositions which can be further cured after being applied to a substrate, making them behave as structural adhesives. More particularly, the present invention provides adhesive and sealant compositions based on a mixture of a telechelic polymer having hydroxyl functionality with a heterotelechelic polymer having both hydroxyl and another type of functionality and a dual curing system such as an isocyanate and a melamine.
Pressure sensitive adhesives based on block copolymers of conjugated dienes and/or vinyl aromatic hydrocarbons are well known. They have the particular advantage that they give an instantaneous bond under light pressure. The limitation of pressure sensitive adhesives is that they lack the cohesive strength to bear high loads. Structural and semi-structural adhesives based on such polymers are also well known. Their advantage is that they cure to give adhesives which can bear quite high loads. Their disadvantage is that they must be applied as liquids in order to achieve good bonding and so the assembly must be fixtured until the adhesives sets, usually by chemical cure, but sometimes by cooling from the melt.
It would be highly advantageous to provide a pressure sensitive adhesive which would give an instantaneous bond while having enough cohesive strength that fixturing requirements would be less demanding or unnecessary and which would cure further upon some subsequent treatment, thereby increasing its cohesive strength so it becomes a structural or semi-structural adhesive. The present invention provides such a composition which is useful in both adhesives and sealants.